Use sliver-based scrolling in more places (#7892)

This patch uses sliver-based two more gallery demos, the stocks example,
in the date picker, and in markdown.

examples/flutter_gallery/lib/demo/date_and_time_picker_demo.dart

@@ -128,13 +128,9 @@ class _DateAndTimePickerDemoState extends State<DateAndTimePickerDemo> {
   Widget build(BuildContext context) {
     return new Scaffold(
       appBar: new AppBar(title: new Text('Date and time pickers')),
-      body: new ScrollableViewport(
-        child: new Container(
+      body: new DropdownButtonHideUnderline(
+        child: new ListView(
           padding: const EdgeInsets.all(16.0),
-          alignment: FractionalOffset.topLeft,
-          child: new DropdownButtonHideUnderline(
-            child: new Column(
-              crossAxisAlignment: CrossAxisAlignment.stretch,
           children: <Widget>[
             new TextField(
               labelText: 'Event name',
@@ -197,8 +193,6 @@ class _DateAndTimePickerDemoState extends State<DateAndTimePickerDemo> {
           ],
         ),
       ),
-        ),
-      ),
     );
   }
 }

examples/flutter_gallery/lib/demo/progress_indicator_demo.dart

@@ -101,7 +101,7 @@ class _ProgressIndicatorDemoState extends State<ProgressIndicatorDemo> with Sing
     return new Scaffold(
       appBar: new AppBar(title: new Text('Progress indicators')),
       body: new Center(
-        child: new ScrollableViewport(
+        child: new SingleChildScrollView(
           child: new DefaultTextStyle(
             style: Theme.of(context).textTheme.title,
             child: new GestureDetector(

examples/stocks/lib/stock_list.dart

@@ -17,17 +17,18 @@ class StockList extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return new ScrollableList(
+    return new ListView.builder(
       key: const ValueKey<String>('stock-list'),
       itemExtent: StockRow.kHeight,
-      children: stocks.map((Stock stock) {
+      itemCount: stocks.length,
+      itemBuilder: (BuildContext context, int index) {
         return new StockRow(
-          stock: stock,
+          stock: stocks[index],
           onPressed: onOpen,
           onDoubleTap: onShow,
           onLongPressed: onAction
         );
-      })
+      },
     );
   }
 }

packages/flutter/lib/src/material/date_picker.dart

@@ -544,34 +544,28 @@ class YearPicker extends StatefulWidget {
 class _YearPickerState extends State<YearPicker> {
   static const double _itemExtent = 50.0;
 
-  List<Widget> _buildItems(BuildContext context, int start, int count) {
+  @override
+  Widget build(BuildContext context) {
+    assert(debugCheckHasMaterial(context));
     final ThemeData themeData = Theme.of(context);
     final TextStyle style = themeData.textTheme.body1;
-    final List<Widget> items = new List<Widget>();
-    for (int i = start; i < start + count; i++) {
-      final int year = config.firstDate.year + i;
+    return new ListView.builder(
+      itemExtent: _itemExtent,
+      itemCount: config.lastDate.year - config.firstDate.year + 1,
+      itemBuilder: (BuildContext context, int index) {
+        final int year = config.firstDate.year + index;
         final TextStyle itemStyle = year == config.selectedDate.year ?
             themeData.textTheme.headline.copyWith(color: themeData.accentColor) : style;
-      items.add(new InkWell(
+        return new InkWell(
           key: new ValueKey<int>(year),
           onTap: () {
             config.onChanged(new DateTime(year, config.selectedDate.month, config.selectedDate.day));
           },
           child: new Center(
-          child: new Text(year.toString(), style: itemStyle)
-        )
-      ));
-    }
-    return items;
-  }
-
-  @override
-  Widget build(BuildContext context) {
-    assert(debugCheckHasMaterial(context));
-    return new ScrollableLazyList(
-      itemExtent: _itemExtent,
-      itemCount: config.lastDate.year - config.firstDate.year + 1,
-      itemBuilder: _buildItems
+            child: new Text(year.toString(), style: itemStyle),
+          ),
+        );
+      },
     );
   }
 }

packages/flutter/lib/src/widgets/scroll_view.dart

@@ -168,6 +168,25 @@ class ListView extends BoxScrollView {
     padding: padding,
   );
 
+  ListView.builder({
+    Key key,
+    Axis scrollDirection: Axis.vertical,
+    bool reverse: false,
+    ScrollPhysics physics,
+    bool shrinkWrap: false,
+    EdgeInsets padding,
+    this.itemExtent,
+    IndexedWidgetBuilder itemBuilder,
+    int itemCount,
+  }) : childrenDelegate = new SliverChildBuilderDelegate(itemBuilder, childCount: itemCount), super(
+    key: key,
+    scrollDirection: scrollDirection,
+    reverse: reverse,
+    physics: physics,
+    shrinkWrap: shrinkWrap,
+    padding: padding,
+  );
+
   ListView.custom({
     Key key,
     Axis scrollDirection: Axis.vertical,
@@ -190,7 +209,7 @@ class ListView extends BoxScrollView {
 
   final double itemExtent;
 
-  final SliverChildListDelegate childrenDelegate;
+  final SliverChildDelegate childrenDelegate;
 
   @override
   Widget buildChildLayout(BuildContext context) {
@@ -317,7 +336,7 @@ class GridView extends BoxScrollView {
 
   final SliverGridDelegate gridDelegate;
 
-  final SliverChildListDelegate childrenDelegate;
+  final SliverChildDelegate childrenDelegate;
 
   @override
   Widget buildChildLayout(BuildContext context) {
@@ -373,7 +392,7 @@ class PageView extends BoxScrollView {
     assert(childrenDelegate != null);
   }
 
-  final SliverChildListDelegate childrenDelegate;
+  final SliverChildDelegate childrenDelegate;
 
   @override
   Widget buildChildLayout(BuildContext context) {

packages/flutter/lib/src/widgets/sliver.dart

@@ -63,7 +63,7 @@ class SliverChildBuilderDelegate extends SliverChildDelegate {
   int get estimatedChildCount => childCount;
 
   @override
-  bool shouldRebuild(@checked SliverChildListDelegate oldDelegate) => true;
+  bool shouldRebuild(@checked SliverChildBuilderDelegate oldDelegate) => true;
 }
 
 // ///

packages/flutter_markdown/lib/src/markdown.dart

@@ -64,15 +64,15 @@ class MarkdownBody extends MarkdownBodyRaw {
   /// by default not using syntax highlighting, but it's possible to pass in
   /// a custom [syntaxHighlighter].
   ///
-  /// Typically, you may want to wrap the [MarkdownBody] widget in a [Padding] and
-  /// a [ScrollableViewport], or use the [Markdown] class
+  /// Typically, you may want to wrap the [MarkdownBody] widget in a
+  /// [SingleChildScrollView], or use the [Markdown] class.
   ///
-  ///     new ScrollableViewport(
-  ///       child: new Padding(
+  /// ```dart
+  /// new SingleChildScrollView(
   ///   padding: new EdgeInsets.all(16.0),
-  ///         child: new Markdown(data: markdownSource)
-  ///       )
-  ///     )
+  ///   child: new Markdown(data: markdownSource),
+  /// ),
+  /// ```
   MarkdownBody({
     String data,
     SyntaxHighlighter syntaxHighlighter,

packages/flutter_markdown/lib/src/markdown_raw.dart

@@ -52,16 +52,16 @@ class MarkdownRaw extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return new ScrollableViewport(
-      child: new Padding(
+    // TODO(abarth): We should use a ListView here and lazily build the widgets
+    // from the markdown.
+    return new SingleChildScrollView(
       padding: padding,
       child: createMarkdownBody(
         data: data,
         markdownStyle: markdownStyle,
         syntaxHighlighter: syntaxHighlighter,
-          onTapLink: onTapLink
-        )
-      )
+        onTapLink: onTapLink,
+      ),
     );
   }
 
@@ -93,17 +93,17 @@ class MarkdownBodyRaw extends StatefulWidget {
   /// highlighting, but it's possible to pass in a custom [syntaxHighlighter].
   ///
   /// Typically, you may want to wrap the [MarkdownBodyRaw] widget in a
-  /// [Padding] and a [ScrollableViewport], or use the [Markdown class]
+  /// a [ScrollableViewport], or use the [Markdown class].
   ///
-  ///     new ScrollableViewport(
-  ///       child: new Padding(
+  /// ```dart
+  /// new SingleChildScrollView(
   ///   padding: new EdgeInsets.all(16.0),
   ///   child: new MarkdownBodyRaw(
   ///     data: markdownSource,
-  ///           markdownStyle: myStyle
-  ///         )
-  ///       )
-  ///     )
+  ///     markdownStyle: myStyle,
+  ///   ),
+  /// ),
+  /// ```
   MarkdownBodyRaw({
     this.data,
     this.markdownStyle,